With my precious golf3 I had the same problem, the moist was creeping in and staying there; even though it got away for day or two after driving for hours with AC set on hot (not too pleasant btw.) it kept getting moist all over again.
Doing something against this may mean replacing the rubber sealings of your doors or similar, but maybe it is just a one time thing for you, in this case one of the things I tried was:
Put some bricks into the oven, set to highest temperature, and leave it there for quite a while. Then quickly put them into some container that withstands the temperature (steel bucket in my case) and put it into the trunk of the car. Removing anything that blocks the air flow (hat shelf, flip over the rear seats if you can). Start car, set AC to really hot, and do not completely close the trunk (just so much that you could stick a scredriver through the gap).
If you get the amount of bricks right, it will quickly heat up the back of the car, causing most moist to evaporate. Hot dehumidified air from the AC will enter at the front and leave at the back, drying out the car pretty well.
The number of bricks depend on your ovens temperature and your cars size. Do not use too many or you might seriously damage something (a lot of stuff in a car doesn't like anything more than 50°C)